Since the 1996 Escherichia coli (E. coli) O157:H7 outbreak, when nearly 10,000 people were sickened, foodborne illness has become a more visible threat to the public health. Almost two decades later, microbial contamination remains one of the most serious challenges for assuring the safety of food supplies. In 2011, the Centers for Disease Control and Prevention (CDC) estimated that roughly 48 million people are sickened by food-borne pathogens each year, including 3,000 cases ending in deaths.
Among all food categories, fruits and vegetables have emerged as the most significant vector of food borne bacterial pathogens because they are frequently consumed raw. Washing is an important step during fresh-cut produce processing as it removes the debris, soils, and produce latex released from the cut edges and maintains quality and shelf life of the final products, and can reduce 1-2 log cfu/g microbial loads.
Maintaining a high level of sanitizer in wash water is a practical challenge to the produce industry due to the rapid reaction of organic matter with sanitizers, especially the widely used hypochlorous acid (chlorine). As a result of its reaction with organic materials present in the wash water, free chlorine concentration usually declines rapidly during fresh produce wash operations.
Determination of the minimum free chlorine concentration needed to prevent pathogen survival/cross-contamination during produce washing is essential for the development of science-based food safety regulations and practices. Although the trend of chlorine concentration-contact time on pathogen inactivation is generally understood, specific information on chlorine and the kinetics of pathogen inactivation (particularly at less than 1 second) is urgently needed by the produce processing industry. However, conventional approaches to obtain this critical data have been unable to adequately measure very rapid responses.
The need exists for a quick and accurate means of determining the adequacy of chlorine wash solutions. The current disclosure is directed to a novel micro-fluidic device that is able to make the required determination in times as short as 0.1 second.
The micro-fluidic mixer described herein comprises one inlet each for bacterial, chlorine and dechlorinating solutions, and one outlet for effluent collection. To determine the kinetics of free chlorine on pathogen inactivation, chlorine solutions of varying concentrations are pumped into the micro-fluidic mixer. A sample bacterial solution is injected into the mixer through a separate inlet.
After mixing, a dechlorinating solution is injected into the mixer to stop the chlorine-pathogen reaction. The effluent is collected and the surviving bacteria cells are enumerated using a modified ‘Most Probable Number’ method. Free chlorine concentration is determined using a standard colorimetric method. The contact time is precisely controlled by adjusting the solution flow rate and quantitatively determined by computational fluid dynamics modeling.